Effect of rice husk biochar on nitrous oxide emission from decomposing hairy vetch in two soils under high-soil moisture condition

Yoshitaka Uchida1, Moe Shimotsuma2

1 Research Faculty of Agriculture, Hokkaido University, Kita9 Nishi9, Kita-ku, Sapporo, Hokkaido 0608589, Japan, www.uchidalab.com, [email protected]

2 Graduate School of Agriculture, Hokkaido University, Kita9 Nishi9, Kita-ku, Sapporo, Hokkaido 0608589, Japan

Abstract

Hairy vetch (Vicia villosa Roth) plants are widely used as green manures. They fix nitrogen (N) and provide a fraction of the fixed N to other crops when they decompose. Thus, green manuring with legumes is considered as an alternative to chemical N fertilizer application. However, N-rich plant residue is also a potential source for nitrous oxide (N2O), a greenhouse gas. On one hand, rice husk biochar is widely used as a soil conditioner in Japan and has been reported as a tool to reduce N2O emissions. The interaction between biochar and N rich composting materials on N2O emission has not been studied well. We conducted a soil core incubation experiment under high soil moisture (~100% WFPS) to investigate the N2O emissions from two soils, i.e., an Andosol and a Fluvisol after application (0.8 kg m-2) of 15N labelled (0.49 atom %) hairy vetch. Additionally, the experiment contains a biochar treatment. The N2O emissions and inorganic-N in soils were monitored for 1.5 month. Generally, the use of biochar suppressed soil NH4+-N concentrations in the Andosol whereas the effect of biochar on NH4+-N was not significant in the Fluvisol. Biochar application did not influence the cumulative N2O emissions but increased the contribution of hairy vetch-N to the cumulative N2O emissions, according to the analyses of N2O-15N. Our study suggests that rice husk biochar is not a good option to mitigate N2O emissions during the decomposition of surface applied hairy vetch, although this study was performed under a laboratory condition without plants. However, the trends of the inorganic-N concentration changes following the addition of hairy vetch and biochar were markedly different between the two soil types. Thus, factors behind the differences need to be further studied.